Friday, June 17, 2011

compressor is engaging and fans are working but Car AC system not taking Freon?

Keep in mind that using an A/C gauge set and seeing BOTH high and low side readings can help in diagnosing the problem when you know what to look for. First, on a 134A system the high and low side service ports are different sizes. AC gauge sets have color coded hoses, the blue color coded hose has a connection that fits on the low side service port and the red hose has a connection that will only fit onto the high side. The yellow hose won’t hook up to anything if just checking the readings; it can be used to connect to a vacuum pump or attached to a refrigerant can or tank.

*Make sure the condenser fan comes on when the readings are being checked.

Below are normal car AC pressure readings with 134A.

  • Normal readings on high and low side with AC OFF (static pressure) – Depends on outside temperature, but normally is between 80-105 PSI
  • Normal low side reading with AC on high speed and MAX & engine at 800-1000 RPM’s – Ranges from 25-35 PSI – Note that on many Chrysler products a normal reading on the low side may be 15-25 PSI
  • Normal high side reading ranges from 200-350 PSI

Don’t assume that if adding little Freon is good that adding a lot is better! Overcharging just a little can decrease the performance of the system and possibly damage the compressor.

Additional Car A/C Info – Troubleshooting Gauge Readings



With the AC on the coldest setting, use a thermometer in a middle vent. Normal vent temperature readings will vary depending on the (ambient) outside temp. The vent temperature should range from around 42-55 degrees in my experience. If normal gauge readings are obtained and the vent air is cold – STOP don’t overcharge the system. The only proper way to remove refrigerant is with a AC recovery machine so if this is being done at home I can’t emphasize enough not to over charge the system. And actually the best way to insure the proper charge is in a system, is to use an AC machine to recover the freon and then evacuate and recharge the system with the correct amount. Most cars have the specified amount on a decal under the hood.

Both sides are lower than normal. Both low and high side readings are lower than normal, this indicates a cars AC system is low on refrigerant and is under-charged.

Both readings are higher than normal. If both low and high side readings are too high, this indicates an overcharged system – too much refrigerant. This also can indicate that the condenser fan is not working, is too slow or the car is overheating and heat is transferring from the radiator to the condenser.

Low side goes into a vacuum and high side is too high. When the low side goes so low that it’s reading shows it is in a vacuum, the most likely cause is a bad expansion valve or blocked orifice tube. Another possibility is a restricted condenser. Blocked condensers are not as common as they used to be but if a compressor fails and comes apart inside the remnants can end up in the condenser causing it to restrict the flow of refrigerant.

Low side is too high and high side is too low. When the compressor clutch is definitely engaged and the low side is high and the high side is low, the most likely cause is that the compressor is failing – it is not pumping sufficiently. Rarely an AC clutch could be slipping but usually this will be accompanied with a squeal or chirp. Also be sure not to overlook the obvious, like a loose belt!



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How to start charging AC:--

The first thing I do is insert a temperature gauge in the middle air vent ( the middle vent gives you the most accurate reading )Start the car and turn the air conditioning to Max and take a temperature reading. This gives you a starting point. After all you want it cooler than it already is or you wouldn't be messing with it.Write down the starting temperature reading for reference later in the repair procedure.
Now you need to look at the compressor to see if the clutch is cycling (clicking on and off). If it is, then most likely you are just a bit low on freon.

You are ready to add refrigerant.

If you haven't already done so, connect your fill line to the low pressure port.

After you connect the center port of your A/C gauges to a can refrigerant, start the vehicle and turn on the air conditioner and set it to MAX. Next slowly open the low pressure manifold and let the freon flow into the system. Run the engine at 1500 rpm to allow the compressor to suck all the freon in. You may need to install a jumper wire at the low pressure switch connector to get the compressor going at first. Do this un till you see 45-55 psi on the gauges at 1500 rpm.


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But if compressor clutch is not cycling on/off then:--

There are three reasons the air conditioning compressor clutch will not engage or turn on.

  1. The compressor clutch solenoid is shot. Replacing the compressor will fix this.
  2. The air conditioning system is very low on freon or empty. Refilling the system required.(Skip to step 10)
  3. There is an electrical problem in the air conditioning circuit. Finding and repairing the short or open in the air conditioning circuit will be necessary.


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    You still could be low on your R-134a. The pressures don't look right to me. It depends on the temperature and your conditions for running your test.

    You AC system doesn't use the "oriface" tube where the freon changes state. It uses the "thermo expansion valve" located on your evaporator core. There is a screen in there just like the orifice tube. The TXV could be plugged or just plain failed.

    Below I have given you a description of operation for your AC system. It explains how the system works. Then I have included a word document that shows what your pressures should read under different conditions. If your not low on your freon, then I suspect your TXV valve may be hanging up.

    AC Description

    Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automotive use. R-134a is a very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.

    A Zexcel rotary vane compressor with variable displacement is used on this model year vehicle. The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat to the refrigerant. The refrigerant is discharged from the compressor, through the discharge hose, and forced to flow to the condenser and then through the balance of the A/C system.

    The A/C system is mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system.

    Compressed refrigerant enters the condenser in a high temperature, high pressure vapor state. As the refrigerant flows through the condenser, the heat of the refrigerant is transferred to the ambient air passing through the condenser. Cooling the refrigerant causes the refrigerant to condense and change from a vapor to a liquid state.

    The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line, to the TXV.

    The TXV is located at the evaporator inlet. The TXV is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the TXV, the pressure on the refrigerant is lowered. Due to the pressure differential on the liquid refrigerant, the refrigerant will begin to boil at the TXV. The TXV also meters the amount of liquid refrigerant that can flow into the evaporator.

    Refrigerant exiting the TXV flows into the evaporator core in a low pressure, liquid state. Ambient air is drawn through the HVAC module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant boil inside of the evaporator core. The boiling refrigerant absorbs heat from the ambient air and draws moisture onto the evaporator. The refrigerant exits the evaporator through the suction line and back to the compressor, in a vapor state, and completing the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.

    The conditioned air is distributed through the HVAC module for passenger comfort. The heat and moisture removed from the passenger compartment will also change form, or condense, and is discharged from the HVAC module as water.


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Normal System Performance Service Stall - L81

Degrees*

Suction*

Discharge*

Outlet*

21°C (70°F)

179-213 kPa (26-29 psi)

958-1275 kPa (139-185 psi)

5-8°C (41-46°F)

27°C (80°F)

172-207 kPa (25-28 psi)

1309-1516 kPa (190-220 psi)

6-9°C (42-48°F)

33°C (90°F)

172-200 kPa (25-27 psi)

1550-2343 kPa (225-340 psi)

7-9°C (45-48°F)

38°C (100°F)

172-200 kPa (25-27 psi)

1895-2343 kPa (275-340 psi)

7-12°C (45-53°F)

*Degrees - If the ambient air temperature is

*Suction - and the low side gauge should read

*Discharge - and the high side gauge should read

*Outlet - and the right center air temperature should be

Important: To ensure accurate pressure and temperature readings make sure the vehicle is properly set up to run the performance test. Refer to vehicle set up section in this manual. ALL TEST PARAMETERS MUST BE FOLLOWED TO OBTAIN ACCURATE READINGS. Confirm system performance by touching the suction and discharge pipes at the compressor. The suction pipe will be cold and the discharge pipe will be hot.

Important: Use a refrigerant identifier to verify refrigerant purity. Non-condensable gases or refrigerant substitutes will affect system pressure/temperature readings.

Normal System Performance 72 Km/h (45 mph)

Degrees*

Suction*

Discharge*

Outlet*

21°C (70°F)

207-220 kPa (30-32 psi)

634-827 kPa (92-120 psi)

6-9°C (42-48°F)

27°C (80°F)

200-213 kPa (29-31 psi)

806-1034 kPa (117-150 psi)

7-10°C (44-50°F)

33°C (90°F)

193-207 kPa (28-30 psi)

999-1206 kPa (145-175 psi)

6-11°C (43-51°F)

38°C (100°F)

193-207 kPa (28-30 psi)

1275-1378 kPa (185-200 psi)

6-13°C (43-55°F)


Normal System Performance Service Stall High Humidity

Degrees*

Suction*

Discharge*

Outlet*

21°C (70°F)

186-193 kPa (27-28 psi)

978-1378 kPa (142-200 psi)

7-8°C (44-46°F)

27°C (80°F)

193-200 kPa (28-29 psi)

1275-1585 kPa (185-230 psi)

8-9°C (46-49°F)

33°C (90°F)

186-193 kPa (27-28 psi)

1640-2480 kPa (238-360 psi)

9-11°C (49-52°F)

38°C (100°F)

186-200 kPa (27-29 psi)

1991-2515 kPa (289-365 psi)

11-13°C (52-56°F)

*Degrees - If the ambient air temperature is

*Suction - and the low side gauge should read

*Discharge - and the high side gauge should read

*Outlet - and the right center air temperature should be

High humidity conditions affect the system performance by increased heat load on the system. This extra heat load will increase the discharge pressure and the outlet temperature. High humidity is defined as a relative humidity higher than 70 percent at 21°C (70°F), 60 percent at 27°C (80°F), 50 percent at 32°C (90°F), and 40 percent at 38°C (100°F).

This chart illustrates the effect the high humidity has on the Saturn air conditioning system. Use this chart to determine the normal system performance under high humidity conditions.

As a general rule, normal system operating under high humidity conditions will produce an outlet temperature of at least 20°F below the ambient air temperature.

General System Condition - Low Refrigerant Charge

Degrees*

Suction*

Discharge *

Outlet *

21-38°C (70-100°F)

Normal to High

Low

Slightly Cool to Warm

Important: The system is operating with a low charge.

Confirm by touching the suction and the discharge pipe at the compressor. The suction pipe will be cool to warm and the discharge pipe will be warm to hot.

The pipe temperatures will vary with he ambient air temperature and the amount of the charge lost. The suction and the outlet temperatures will be warmer as more refrigerant is lost or ambient air temperature increases.

Leak test all the components and connections.

If the refrigerant charge level is unknown, reclaim, evacuate and recharge the system with 0.95 kg (2.09 lb) of R-134a refrigerant.

Run another performance test.

Key: Poor Cooling at Higher Ambients.

*Degrees - If the ambient air temperature is

*Suction - and the low side gauge should read

*Discharge - and the high side gauge should read

*Outlet - and the right center air temperature should be


General System Condition Refrigerant/Oil Overcharge

Degrees*

Suction*

Discharge*

Outlet*

21-38°C (70-100°F)

Normal to Slightly High

High

Cool to Warm

Important: The System may be operating in an overcharged condition.

Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be cool and the discharge pipe will be vary hot.

An overcharged condition will generate a poor and/or intermittent cooling complaint at higher ambient air temperatures. Intermittent complaints are caused by the pressure switch cycling the compressor ON and OFF.

Reclaim the system using an approved recovery system. Evacuate and recharge the system with 0.95 kg (2.09 lb) of R-134a refrigerant.

Run another performance test.

An oil overcharge can occur if a compressor change is made without proper oil balancing. Review the vehicle service history for compressor service.

Key: The high pressure switch cycles the compressor on and off at high ambient air temperatures.


Specific System Condition-Compressor No-Pump - L81

Degrees*

Suction*

Discharge*

Outlet*

21-38°C (70-100°F)

483-689 kPa (70-100 psi)

483-689 kPa (70-100 psi)

21-38°C (70-100°F)

Important: Ensure that the manifold gauge set valves are closed.

Important: Most likely the vanes are not extending to the cylinder walls.

Run the engine at 2,000 RPM and cycle the compressor ON and OFF two or three times.

If the pressure remains static, engage the compressor and snap the engine throttle two or three times.

If the pressure still remains static, replace the compressor.

After the repair, return to the diagnostic flow chart.

Key: No change in the suction and the discharge pressures with the compressor engaged. The gauge pressures will be almost equal.

*Degrees - If the ambient air temperature is

*Suction - and the low side gauge should read

*Discharge - and the high side gauge should read

*Outlet - and the right center air temperature should be


Specific System Condition - Compressor at Minimum Displacement

Degrees*

Suction*

Discharge*

Outlet*

21°C (70°F)

317-358 kPa (46-52 psi)

717-861 kPa (104-125 psi)

17-21°C (62-69°F)

27°C (80°F)

358-400 kPa (52-58 psi)

854-1171 kPa (124-170 psi)

18-23°C (64-73°F)

33°C (90°F)

400-455 kPa (58-66 psi)

1013-1240 kPa (147-180 psi)

21-26°C (70-79°F)

38°C (100°F)

455-565 kPa (66-82 psi)

1144-1550 kPa (166-225 psi)

27-32°C (81-90°F)

Important: The compressor may be at minimum displacement.

This condition will be most noticeable at high ambients.

Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be warm and the discharge pipe will be warm to hot.

Confirm the charge level before replacing the compressor.

After the repair, return to the diagnostic flow chart.

Key: Increased suction pressure for a relatively low discharge pressure and high outlet temperatures.

*Degrees - If the ambient air temperature is

*Suction - and the low side gauge should read

*Discharge - and the high side gauge should read

*Outlet - and the right center air temperature should be


Specific System Condition - Compressor at Maximum Displacement

Degrees*

Suction*

Discharge*

Outlet*

21°C (70°F)

110-124 kPa (16-18 psi)

1164-1240 kPa (169-180 psi)

3-6°C (37-42°F)

27°C (80°F)

138-158 kPa (20-23 psi)

1378-1654 (200-240 psi)

3-8°C (37-46°F)

33°C (90°F)

165-172 kPa (24-25 psi)

1598-2274 kPa (232-330 psi)

6-9°C (42-49°F)

38°C (100°F)

179-186 kPa (26-27 psi)

1902-2412 kPa (276-350 psi)

8-11°C (46-51°F)

Important: The compressor may be at maximum displacement.

This condition will be most noticeable at low ambients.

Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be very cold and the discharge pipe will be hot.

This condition could generate an intermittent cooling complaint along with reduced air flow because of evaporator freeze up at lower ambient air temperatures.

Replace the compressor.

After the repair, return to the diagnostic flow chart.

Key: Lower than normal suction pressure and outlet temperature at lower ambients and higher than normal discharge pressures.

*Degrees - If the ambient air temperature is

*Suction - and the low side gauge should read

*Discharge - and the high side gauge should read

*Outlet - and the right center air temperature should be


Specific System Condition - TXV Restricted

Degrees*

Suction*

Discharge*

Outlet*

21°C (70°F)

200-213 kPa (27-29 psi)

806-1068 kPa (117-155 psi)

11-12°C (51-53°F)

27°C (80°F)

172-200 kPa (25-27 psi)

1123-1378 kPa (163-200 psi)

8-11°C (47-52°F)

33°C (90°F)

158-179 kPa (23-26 psi)

1337-1929 kPa (194-280 psi)

9-13°C (49-55°F)

38° (100°F)

165-179 kPa (24-26 psi)

1660-2412 kPa (241-350 psi)

9-14°C (48-58°F)

Important: The degree of restriction will alter temperature and pressure readings.

Important: The thermal expansion valve (TXV) may be restricted.

Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be warm to cool at low ambients and cool to cold at high ambients. The discharge pipe will be warm to hot.

This condition can lead to compressor chatter due to lack of oil.

Replace the TXV.

After the repair, return to the diagnostic flow chart.

Key: Low suction pressure and higher than normal outlet air temperatures.

*Degrees - If the ambient air temperature is

*Suction - and the low side gauge should read

*Discharge - and the high side gauge should read

*Outlet - and the right center air temperature should be


Specific System Condition - TXV Open

Degrees*

Suction*

Discharge*

Outlet*

21°C (70°F)

186-207 kPa (27-30 psi)

1123-1178 kPa (163-171 psi)

8-11°C (47-51°F)

27°C (80°F)

193-220 kPa (28-32 psi)

1282-1309 kPa (186-190 psi)

9-12°C (48-54°F)

33°C (90°F)

220-255 kPa (32-37 psi)

1447-1723 kPa (210-250 psi)

8-17°C (47-63°F)

38° (100°F)

248-317 kPa (36-46 psi)

1778-2136 kPa (258-310 psi)

14-18°C (58-64°F)

Important: The thermal expansion valve (TXV) may be open.

Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be cool to cold and the discharge pipe will be warm to hot.

This condition can lead to compressor chatter due to oil being flushed from the compressor.

Replace the TXV.

After the repair, return to the diagnostic flow chart.

Key: Higher than normal suction pressure, and higher than normal outlet temperatures.

*Degrees - If the ambient air temperature is

*Suction - and the low side gauge should read

*Discharge - and the high side gauge should read

*Outlet - and the right center air temperature should be


General System Condition - TXV Closed

Degrees*

Suction*

Discharge*

Outlet*

21-38°C (70-100°F)

0-34 kPa (0-5 psi)

482-689 kPa (70-100 psi)

21-38°C (70-100°F)

Important: The thermal expansion valve (TXV) may be closed.

Confirm by touching the suction and the discharge pipes at the compressor. The suction pipe will be warm and the discharge pipe will be warm to hot.

This condition may cause compressor damage due to the lack of oil circulation. Check the compressor operation.

Replace the TXV.

After the repair, return to the diagnostic flow chart.

Key: Near vacuum for suction pressure, low discharge pressure, and right center air grill near ambient.

*Degrees - If the ambient air temperature is

*Suction - and the low side gauge should read

*Discharge - and the high side gauge should read

*Outlet - and the right center air temperature should be


General System Condition - High or Low Side Restrictions

Degrees*

Suction*

Discharge*

Outlet*

21-38°C (70-100°F)

Low

Low

Cool to Warm

Important: Confirm the condition by a thorough physical and visual inspection of all lines and components.

If the restriction is between the compressor and the condenser, the discharge pressure will be higher than normal.

The temperature will be much colder on the down stream side of the restriction. Also look for possible frost.

Replace the restricted part.

After the repair, return to the diagnostic flow chart.

Key: Temperature drop across restriction in line or component.

*Degrees - If the ambient air temperature is

*Suction - and the low side gauge should read

*Discharge - and the high side gauge should read

*Outlet - and the right center air temperature should be

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